Mast cells are known for their involvement in allergic reactions where they secrete many vasoactive and proinflammatory molecules. Mast cells are located perivascularly close to nerve endings and are activated by nerve stimulation. Acute psychological stress by immobilization triggered dura mast cell degranulation and resulted in cerebrospinal fluid (CSF) increase of rat mast cell protease (RMCP) I. These effects were inhibited by pretreatment with neutralizing antiserum for corticotropin-releasing hormone (CRH), treatment with the CRH-receptor antagonist Antalarmin or treatment neonatally with capsaicin to deplete sensory nerve fibers of their substance P (SP) content. Intradermal administration of CRH, and its structural analog urocortin, degranulated skin mast cells and increased vascular permeability; this process was dependent on mast cells and was mediated by specific CRH receptors. We are hypothesizing that CRH released outside the blood-brain barrier (BBB), directly or through SP, leads to dura mast cell degranulation and release of vasodilatory molecules, such as histamine. This action could help explain the pathophysiology of migraines and could serve as a possible model for the screening of relevant drugs. We will test this premise by investigating: (a) the effect of CRH and urocortin on dura mast cell degranulation and vasodilation by measuring Evans blue of 125I-BSA extravasation in the dura of C57 BL/6J mice; vasodilation will also be ascertained with the use of a fiberoptic probe designed to detect temporal blood flow, blood volume and oxygenation, while jugular venous samples will be assayed for histamine and methylistamine; (b) the effect of immobilization stress on dura mast cell degranulation and dura vasodilation with or without pretreatment with the CRH receptor antagonist Astressin or the nonpeptide NK1-receptor antagonist SR 140.333; (c) dura vasodilation as in (a-b) in W/Wv mast cell deficient mice to determine the need for mast cells, in CRH knock-out mice to examine the role of CRH, as well as in SP and NK1-receptor knock-out mice to investigate the need for SP. These studies will help us understand how certain neuropeptides released under stress trigger dura mast cell secretion leading to vasodilation. They may also help explain some key events in the pathophysiology of migraines, the clinical symptoms of which are often precipitated by stress.